Fertiliser spreaders of the prior art typically move fertiliser material from a bin or hopper to a spreading means, typically a spinner, blower or similar, by means of a conveyor. The rate at which the fertiliser is deposited onto the land is controlled by the speed of the conveyor relative to the speed of the vehicle over the land.
A problem with prior art fertiliser spreaders is the variation in the rate at which fertiliser is spread onto the ground when the spreader is either climbing or descending sloping or hilly terrain. The variation is dependant on the type of conveyor used, but generally the spread rates of even the best spreaders may vary by around 40% when the spreader is climbing or descending gradients of around 1:4.
The degree of variation may be of approximately the same magnitude whether the spreader is ascending or descending the hill.
The majority of fertilizer spreaders have the spreading means located at the rear of the vehicle. When ascending, fertiliser tends to flow down the conveyor from the bin or hopper to the spreading means, increasing the rate at which the fertilizer is deposited. When descending, the fertiliser tries to flow against the direction of the conveyor, reducing the spread rate.
In some cases the variation may not be noticed by the operator of the spreader as the increased fertiliser deposited when the spreader is ascending a slope may balance the decreased amount spread when descending. Nevertheless, it is recognised that the consequences of this degree of variation in the amount of fertilizer deposited on the ground may be significant.
Areas of land which have been overfertilised may not absorb the excess fast enough to prevent fertiliser from entering the groundwater. Some districts restrict spreading of fertiliser within a certain radius of lakes or rivers for this reason.
Areas of land which have been underfertilised may not grow optimally.